The standard high pressure sodium (HPS) arc discharge lamp is a very efficient source of visible light and has the highest efficacies (lumens per watt) of any commercially available lamp. However, the HPS lamp has found only limited application, due in part to the special starting and ballasting requirements. A high voltage pulse on the order of 2000 volts is required for cold starting of prior art HPS lamps. Voltages as high as 10 kilovolts are required for hot restart. Typically, there is a delay of several minutes before a hot HPS lamp can be restarted at 2000 volts. For outdoor lighting and for some industrial applications in developed countries, the starting and ballasting requirements do not deter use. For other applications and particularly in underdeveloped countries, there is a reluctance to replace incandescent lamps with the more efficient HPS lamps. In order to gain more widespread acceptance, it is desirable to simplify the starting and ballasting requirements of HPS lamps. New starting techniques should provide fast starts and restarts, as well as simplicity and low cost.
An incandescent lamp utilizing a gaseous fill that is enriched with metallic vapors is disclosed in French Publication No. 2,346,852, dated Oct. 28, 1977. Although the French publication suggests a fill material including sodium, the disclosed lamp operates as a gas-enhanced incandescent lamp and not as an arc discharge lamp. A high pressure sodium lamp utilizing a tungsten ignition wire within the discharge tube is shown by de Groot et al in The High Pressure Sodium Lamp. Philips Technical Library, 1986, page 184. The tungsten ignition wire is connected to only one of the two electrodes in the discharge tube and operates by reducing the gap in which initial breakdown occurs. A high pressure sodium discharge lamp having a multiple turn tungsten wire starting aid wound around the outside of the arc tube is disclosed in U.S. Pat. No. 4,037,129 issued July 19, 1977 to Zack et al. During starting, the tungsten starting aid is connected to the same voltage as one of the arc tube electrodes.
It is a general object of the present invention to provide high pressure arc discharge lamps having improved electrical characteristics, not necessarily improved light output.
It is another object of the present to provide high pressure arc discharge lamps that can be started without high voltage starting pulses.
It is another object of the present invention to provide high pressure sodium arc discharge lamps that can be started with voltages that do not exceed the available AC supply voltage.
It is a further object of the present invention to provide high pressure sodium arc discharge lamps that have fast starting and fast hot restarting characteristics.
It is yet another object of the present invention to provide high pressure sodium arc discharge systems which are simple in construction and low in cost.